In Odoo/OpenERP we can inherit or use existing modules object/class/model and views. We can also inherit single field of existing modules. The question is why we need such inheritance.

The purpose of inheritance or why we need inheritance is given below:

1. To change attributes of some fields which exists on existing/custom model (e.g. making fields readonly,invisible)

2. To add/modify/delete old or new fields in existing/custom model (e.g. Product, Sales, HR, Fleet Management, Attendance modules model etc)

3. We can also add buttons in already existing/custom model (form and tree) view by using inheritance

To model inheritance

class groups(models.Model):
 _inherit = 'res.groups'
 # we inherited res.groups model which is Odoo/OpenERP built in model and created two fields in that model.
 field_1 = fields.Char(required=True,string="Field One")
 field_2 = fields.Boolean(default=False,string="Field Two") 

To view inheritance

<openerp>
    <data>
        <record model="ir.ui.view" id="res_group_form_view_inherited">
            <field name="name">res.group.form.view.inherited</field>
            <field name="model">res.groups</field>
            <field name="inherit_id" ref="base.view_groups_form" />
            <!-- <field name="groups_id" eval="[(6, 0, [ref('obe_core.obe_coordinator')])]"/> -->
            <field name="priority" eval="15"/>
            <field name="arch" type="xml">

                <xpath expr="//field[@name='name']" position="after">
                    <field  name="field_1"/>
                </xpath>                
                
                <xpath expr="//field[@name='user_name']" position="after">
                    <field  name="field_2"/>
                </xpath>        

            </field>                               
        </record>
    </data>
</openerp> 

To understanding of code with description please visit: http://learnopenerp.blogspot.com/2018/01/inheritance-in-models-and-views.html

Nice post.

https://360digitmg.com/python-typeerror-nonetype-object-is-not-subsriptable

how can i add more fields to inherit model